The present invention relates generally to the field of integrated circuits and, in particular, to integrated circuits using optical Waveguide interconnects formed through a semiconductor wafer and methods for forming same.
Electrical systems typically use a number of integrated circuits that are mounted on a printed circuit board. The individual integrated circuits of the system are typically fabricated on different wafers. Each wafer is tested and separated into individual dies or chips. Individual chips are then packaged as individual integrated circuits. Each integrated circuit includes a number of leads that extend from the packaging of the circuit. The leads of the various integrated circuits, are interconnected to allow information and control signals to be passed between the integrated circuits such that the system performs a desired function. For example, a personal computer includes a wide variety of integrated circuits, e.g., a microprocessor and memory chips, tat are interconnected on one or more printed circuit boards in the computer.
While printed circuit boards are useful for bringing together separately fabricated and assembled integrated circuits, the use of printed circuit boards creates some problems which are not so easily overcome. For example, printed circuit boards consume a large amount of physical space compared to the circuitry of the integrated circuits which are mounted to them. It is desirable to reduce the amount of physical space required by such printed circuit boards. Further, assuring the electrical integrity of interconnections between integrated circuits mounted on a printed circuit board is a challenge. Moreover, in certain applications, it is desirable to reduce the physical length of electrical interconnections between devices because of concerns with signal loss or dissipation and interference with and by other integrated circuitry devices.
A continuing challenge in the semiconductor industry is to find new, innovative, and efficient ways of forming electrical connections with and between circuit devices which are fabricated on the same and on different wafers or dies. Relatedly, continuing challenges are posed to find and/or improve upon the packaging techniques utilized to package integrated circuitry devices. As device dimensions continue to shrink, these challenges become even more important.
For reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved technique for interconnecting individual integrated circuits in an electronic system.
The above mentioned problems with integrated circuits and other problems are addressed by the present invention and will be understood by reading and studying the following specification. Integrated circuits are described which use optical waveguides that extend through the thickness of a semiconductor substrate or wafer so as to allow communication between integrated circuits formed on opposite sides of a single wafer, on opposite sides of two wafers that are bonded together, formed on wafers in a stack that are bonded together, or other appropriate configuration of wafers.
In particular, in one embodiment, a method for interconnecting first and second integrated circuits is provided. The first integrated circuit is formed on a working surface of a fist semiconductor substrate. At least one high aspect ratio hole is formed through the first semiconductor substrate. The high aspect ratio hole is lined with a material having a high reflectivity for light to form an optical waveguide. The first integrated circuit is coupled to the second integrated circuit through the optical waveguide. In one embodiment, the second integrated circuit is formed on a second surface of the first semiconductor substrate, opposite the working surface of the first semiconductor substrate. In another embodiment, the second integrated circuit is formed on a working surface of a second semiconductor substrate. The second semiconductor substrate is bonded to the first semiconductor substrate such that the first and second integrated circuits are coupled together through the optical waveguide in the first semiconductor substrate. In another embodiment, the surfaces of the first and second semiconductor substrates that are bonded together are located on sides of the first and second semiconductor substrates that are opposite the working surfaces of the first and second semiconductor substrates, respectively.
In another embodiment, an electronic system is provided. The electronic system includes at least one semiconductor wafer. The electronic system includes a number of integrated circuits. At least one integrated circuit is formed on the at least one semiconductor wafer. The at least one semiconductor wafer includes at least one optical waveguide formed in a high aspect ratio hole that extends through the thickness of the at least one semiconductor wafer. Further, at least one optical transmitter and at least one optical receiver are associated with the at least one optical waveguide. The optical transmitter and optical receiver transmit optical signals between selected integrated circuits of the electronic system.
In another embodiment, an integrated circuit is provided. The integrated circuit includes a functional circuit formed on a wafer. A number of optical waveguides are formed in high aspect ratio holes that extend through the wafer. The optical waveguides include a highly reflective material that is deposited so as to line an inner surface of the high aspect ratio holes.
In another embodiment, a method for forming an integrated circuit in a semiconductor wafer with an optical waveguide that extends through the semiconductor wafer is provided. A functional circuit is formed in a first surface of a semiconductor wafer. A number of etch pits are formed in the first surface of the semiconductor wafer at selected locations in the functional circuit An anodic etch of the semiconductor wafer is performed such that high aspect ratio holes are formed through the semiconductor wafer from the first surface to a second, opposite surface. A highly reflective layer of material is formed on an inner surface of the high aspect ratio holes such that the holes have an opening extending through the semiconductor wafer with a diameter that is at least three times the cut-off diameter. The optical fiber is selectively coupled to the functional circuit.
In another embodiment, a method for forming an optical waveguide through a semiconductor substrate is provided. The method includes forming at least one high aspect ratio hole through the semiconductor substrate that passes through the semiconductor substrate from a first working surface to a surface opposite the first working surface. Further, the high aspect ratio hole is lined with a material having a high reflectivity for light. In one embodiment, the at least one high aspect ratio hole is etched in the semiconductor substrate using an anodic etch. In one embodiment, etch pits are formed in the working surface of the semiconductor substrate prior to the anodic etch such that the at least one high aspect ratio hole is formed at the location of the etch pits. In one embodiment, the high aspect ratio holes are lined with a layer of tungsten and a layer of aluminum. In one embodiment, the tungsten layer is formed using a silicon reduction process and a silane reduction process. In one embodiment, the high aspect ratio hole is lined with a layer of aluminum material. In one embodiment, the layer of aluminum material has a thickness of approximately 300 angstroms. In one embodiment, the optical waveguide includes an opening extending through the semiconductor substrate with a cross-sectional diameter of at least three times the cut-off diameter.